Vexing Puzzle Mystery Cache

The cache is not at the given coordinates. These coordinates, however, mark a convenient parking area from which to begin your quest. There's a nice set of trails that will lead you to the cache once you puzzle out where to go.

A young scientist with an interest in vexillology recently checked out the complete works of Sir Charles Wheatstone. Tucked between the pages of the weighty tome, was an envelope containing a strange photograph with a coded message written on the back.

Can you help our intrepid scientist/explorer decrypt the message and find the hidden treasure?

The Photo:

The message:

YK TS ZD SB YE KY ZW TF ZO QU YH

GT YT GT TZ NM PT IU MQ TZ SI NM

PT YE PS FT MY BZ TS EP QI SP YH

GT YP QI SP TW CK ER GU YM

You can check your answers for this puzzle on Geochecker.com.

The puzzle solution coordinates may be about 10m too far south. Future searchers might add 0.004 to north and 0.005 to west -- or -- use the large object mentioned in the hint for reference.

Cache has Rockefeller Permit #RSPP07